Method of producing large thin-walled sand castings of high internal integrity

ABSTRACT

A process for high integrity castings of metals and their alloys includes the steps of providing at least a sand mold at desired elevated temperatures, delivering a molten metal into the mold, and supplying a predetermined amount of coolant to contact the surfaces of the casting at desired rates, times, and durations to achieve an acceptable level of progressive solidification from the distal end of the casting towards the riser until the casting has reached desired temperatures.

GRANT STATEMENT

None.

FIELD OF THE INVENTION

The present invention relates to the casting of metals, morespecifically, to a novel method of producing sand castings in hot moldscoupled with progressive cooling (HMPC).

BACKGROUND OF THE INVENTION

Large thin-walled shape castings free from shrinkage porosity aredifficult to make, especially those with lengths much greater than theirthickness. One example is thin-walled plate-shaped castings with lengthsthat are orders of magnitude greater than their wall thickness. Thelength of such castings is limited by the fluidity of the metal. Theinternal quality of such castings is affected by the feeding of thesolidification shrinkage by a feeder.

Forging is capable of producing porosity-free thin-walled plate-shapedparts. Pores that form during solidification can be closed by plasticdeformation during forging. However, forging is incapable of makingparts of complex geometry. The costs associated with forgings are muchhigher than those of castings. In addition, forging is good only formanufacturing small parts.

Continuous casting and direct-chill casting processes are capable ofmaking billets free from shrinkage porosity but are incapable of makingthin-walled shape castings of complex geometry [1].

High-pressure diecasting (HPDC) is a process that has been widely usedfor making large thin-walled shape castings [2]. High pressure is usedfor driving a molten metal into the thin-walled cavity in strong metalmolds. The internal quality of the thin-walled castings made by the HPDCprocess is usually poor due to the entrapped gases and oxides during theturbulent mold filling process associated with the HPDC process [3-4].Furthermore, solidification shrinkage in thin-walled shape casting isdifficult to feed [5]. As a result, porosity is a common defect inproducts made using the HPDC process, including semisolid recasting,indirect squeeze casting, or even direct squeeze casting, which isdifficult to utilize in making complexly shaped thin-walled parts. Inaddition, the size of a casting that can be produced by the HPDC processis limited by the size and properties of the metal mold and the fluidityof the alloy [2, 6-7].

Gravity casting processes using metal molds have issues with moldfilling for producing large thin-walled shape castings [6] and shrinkagefeeding problems [8]. The minimal wall thickness that can be made usingthese processes is much greater, and the maximum size of a casting ismuch smaller than those made using HPDC. These processes are difficultfor manufacturing large thin-walled castings of high internal integrity.

Sand casting is probably the only cost-effective casting process that iscapable of producing porosity-free shape castings of a large size and acomplex geometry. However, the minimal wall thickness of a castingproduced by the sand casting process is much greater than that by HPDCdue to fluidity issues.

Porosity in a sand casting consists of gas porosity and shrinkageporosity [5]. Gas porosity can be removed by careful degassing. Tominimize shrinkage porosity, risers must be used. The feeding distanceof a riser is about 2 times the wall thickness for a steel casting andabout up to 10 times the wall thickness for an aluminum casting [9]. Asa result, a large number of risers must be used to make a largethin-walled casting free from shrinkage porosity, leading to extremelylow metal yield per mold. These risers must be machined out, resultingin extra labor and costs.

Forced directional solidification from the distal end of the casting toits riser/feeder could be useful in extending the feeding length of theriser. For example, the use of metal chills extends the feeding distanceof a riser by two times the wall thickness of a casting [9]. Still, suchan increase in feeding distance by using chills is very limited.

U.S. Pat. No. 7,216,691 to Grassi et al. discloses an ablation castingtechnology which uses a soluble binder for making sand molds and nozzlesoutside of the molds for spraying a liquid solvent over the molds todissolve the soluble binder, to ablate away the molds and to cool thesolidifying casting progressively from the distal end of the casting tothe feeder. Such a technology is capable of extending the feedingdistance of the feeder, but a unique soluble binder must be used forthis technology.

So far, research on ablation casting technology has been focused onshapes of castings that have no issues fluidity and shrinkage porosity[10-21]. The castings tested are either of a relatively thick wall orwith risers. Little work on thin-walled casting is available inliterature. Porosity was found in A356 alloy castings with an earlyapplication of ablation cooling, but a significant amount of porositywas formed in both the sand casting and the castings ablation cooled atlater stages of solidification [16]. Porosity was also found in aluminummatrix composite castings solidified under ablation cooling conditions[13].

Therefore, there is a need to develop a novel casting process that iscapable of producing thin-walled shape castings free from shrinkageporosity. Such castings would have mechanical properties approachingthose of forgings made from the same alloy.

There is also a need to develop a novel casting process that is capableof forming thin-walled shape castings of high internal quality withoutthe need of risers.

There is also a need to develop a process that is capable of producinglarge sand castings with comparable wall thicknesses and greater sizesthan those of HPDC castings.

Furthermore, there is a need to develop a process that is capable ofmanufacturing large thin-walled castings with controlled internalporosity distribution for weight reduction.

Furthermore, there is also a need to develop a process that is capableof using ablation cooling with water spray but does not require the useof a water-soluble binder to make sand molds.

SUMMARY OF THE INVENTION

The invention provides a hot mold progressive cooling (HMPC) sandcasting process for the fabrication of thin-walled shape castings ofhigh internal integrity. The process includes the steps of providing atleast one sand mold held at elevated temperatures, introducing a moltenalloy into the mold cavity, maintaining the mold or molds abovepredetermined temperatures while the molten alloy undergoessolidification within the mold cavity, and progressively cooling thesolidifying alloy using a coolant from the distal end of the castingtowards the riser or feeder until the casting has reached desiredtemperatures.

In an embodiment of the present invention, a process for reducing theuse of risers or feeders for the fabrication of thin-walled shapecastings of high internal integrity is provided. The process includesthe steps of providing at least one mold held at elevated temperatures,introducing a molten alloy into the mold cavity, maintaining the mold ormolds above predetermined temperatures while the molten alloy undergoessolidification within the mold cavity, and progressively cooling thesolidifying alloy using a coolant from the distal end of the castingtowards the downsprue until the entire casting is completely solidified.

In another embodiment of the present invention, a process for thefabrication of extremely large thin-walled shape castings of highinternal integrity is provided. The process includes the steps ofproviding at least one mold held at elevated temperatures, introducing amolten alloy into the mold cavity, maintaining the mold or molds abovepredetermined temperatures to ensure the fluidity of the alloy to fillthe mold cavity, and progressively cooling the solidifying alloy using acoolant from the distal end of the casting towards the feeder/downsprueuntil the entire casting is totally solidified.

In yet another embodiment of the present invention, a process for thefabrication of thin-walled shape castings with controlled porositydistribution is provided. The process includes the steps of providing atleast one mold held at various locally elevated temperatures,introducing a molten alloy into the mold cavity, maintaining the mold ormolds above predetermined temperatures while the molten alloy undergoessolidification within the mold cavity, and progressively cooling thesolidifying alloy using a coolant with varying speeds from the distalend of the casting towards the downsprue until the entire casting istotally solidified.

BRIEF DESCRIPTION OF THE DRAWINGS

The patent or application file contains at least one drawing executed incolor. Copies of this patent or patent application publication withcolor drawing(s) will be provided by the Office upon request and paymentof the necessary fee.

FIG. 1 is a schematic view of a layout of one embodiment of the presentinvention.

FIG. 2 is a schematic view of a layout of one embodiment of the presentinvention.

FIG. 3 is a schematic view of a casting, the molds and the locationswhere tensile specimens are taken from the plate-shaped casting.

FIG. 4 depicts the relationship between the solid fraction and thetemperature of the A356.2 alloy.

FIGS. 5A, 5B, and 5C show the cooling curves, the evolution of fractionsolid in a sand casting on cooling, and an SEM image of the fracturedsurface of a tensile specimen, respectively.

FIGS. 6A, 6B, and 6C show the cooling curves of a sand casting and aHMPC casting, the evolution of fraction solid in the HMPC casting oncooling, and an SEM image of the fractured surface of a tensile specimentaken from the HMPC casting, respectively.

FIGS. 7A, 7B, and 7C show the cooling curves of a sand casting and aHMPC casting, the evolution of fraction solid in the HMPC casting oncooling, and an SEM image of the fractured surface of a tensile specimentaken from the HMPC casting, respectively.

FIGS. 8A, 8B, and 8C show the cooling curves of a sand casting and aHMPC casting, the evolution of fraction solid in the HMPC casting oncooling, and an SEM image of the fractured surface of a tensile specimentaken from the HMPC casting, respectively.

FIG. 9 is a photograph showing the HMPC process in operation.

FIG. 10 is a photograph showing two castings made by the HMPC process.

FIG. 11 shows the tensile strength of selected castings and forgings.

FIG. 12 shows the elongation of selected castings and forgings.

DETAILED DESCRIPTION OF THE INVENTION

Unless otherwise defined, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which this invention belongs. All publications, patentapplications, patents, and other references mentioned herein areincorporated by reference in their entirety.

The present invention is also explained in detail in the articlerecently published in an international journal [22].

In a preferred embodiment, the present invention relates to a method ofmanufacturing large thin-walled sand castings with high internalintegrity using hot mold with progressive cooling (HMPC) process. Theterm “large thin-wall” defines the shape of a casting when its length orwidth, whichever is the greatest, is 4 times to orders of magnitudegreater than its average wall thickness. Such a casting is unable to befed using a single riser by prior art in the metal casting industry. Theconventional wisdom in the art of metal casting is that the feedingdistance of a riser is 2.5 times the thickness of steel castings and isless than 10 times the thickness of aluminum castings [8]. The term“high internal integrity” refers to the internal quality of a castingthat is free from shrinkage porosity. By such a definition, largethin-walled castings of high internal integrity are unable to bemanufactured using a single riser by prior art because thesolidification shrinkage of the casting cannot be fed, resulting in theformation of shrinkage porosity in the casting. Hot molds in the presentinvention include those that are heated up to elevated temperaturesusing known conventional technologies in the metal casting industry. Hotmolds also include molds that contain exothermic materials or insulatingmaterials at their localities. For example, molds can be heated up usingfurnaces, ovens, or infrared lamps. Exothermic materials can be placedin certain locations in a mold to heat up the mold locally. Insulationmaterials can be placed in certain locations to maintain the localtemperatures in the molds. The term “progressive cooling” refers tocooling methods that maintain the freezing front movement with selectedspeeds, which are under control, from the distal end of the casting tothe riser, feeder, or downsprue. The uniqueness of this presentinvention is in the use of combined technologies in mold heating andcasting cooling to ensure the ease at which molten metal can fill alarge thin-walled mold cavity and feed the solidification shrinkageduring the solidification of the molten metal.

Cavities for a large thin-walled casting are usually difficult to fillby molten metal because the molten metal tends to solidify when it flowsinto the cold cavity. The length of a thin-walled cavity that a moltenmetal can flow before being frozen depends on the size of the flowchannel, the temperature of the molten metal and the molds, the pressuredriving the flow, and other factors. Molds with higher temperaturesallow a molten metal to flow a greater length than molds with lowertemperatures. Given sufficient pressure, a molten metal can flow to filla cavity of any length provided that the mold temperatures are higherthan the freezing temperature of the molten metal and the channelthickness is not extremely thin. Still, the metal casting industryprefers not using molds of high temperatures partly because the hotmolds slow down the solidification rates in the casting, promoteone-dimensional heat transfer from surfaces to the centerline of thethin-wall, and lead to increased formation of porosity in the finalproduct. Molds of high temperatures are usually used for making largethin-walled castings that have no strict requirements on their internalquality.

The new idea of this present invention is to use the hot molds tofacilitate the mold filling of a molten metal and to maintain thesolidifying metal at temperatures where the colder freezing front can befed by hotter metal ahead of the front by either a liquid feeding ormass feeding mechanism. To keep the freezing front sufficiently fed, thefreezing front has to travel from the distal end of the casting to thefeeder/downsprue while the solidifying metal ahead of the front is stillat adequate temperatures. Such a condition has to be satisfied byforcing the freezing front to travel through the casting within the timeframe where shrinkage feeding can still be maintained. The presentinvention deals with the utilization of technologies for mold heatingand progressive cooling to produce large thin-walled shape castings ofhigh internal integrity. The use of hot molds is 1) to ensure thatextremely large thin-walled cavities can be filled by a molten metal ormaterial, 2) to ensure that the solidifying metal in predeterminedregions of the mold can be maintained at predetermined temperaturesbefore the coolant is applied locally, and 3) to allow sand mold withcertain conventional binders to be used for controlled penetration ofthe coolant to cool the solidifying casting. The use of hot moldtechnology combined with the progressive cooling technology is to ensurethat shrinkage porosity can be totally avoided in the solidifyingcasting. Furthermore, a controlled mold temperature distributioncombined with a controlled variable progressive cooling can be used forcontrolling porosity distribution in a casting so that critical areas inthe casting are porosity free but non-critical areas contain acontrolled amount of porosity, leading to a mass reduction of theresultant casting.

FIG. 1 illustrates a method of one embodiment of the present inventionon the production of large thin-walled sand castings with high internalintegrity using HMPC technology. Sand molds 12 and 16 are made with orwithout flasks. The mold, 12 or 16, is composed of an aggregate and abinder that are conventionally used for making green sand molds, and canbe made using conventional mold making methods including, but notlimited to, mold making machine, sand blower, 3D printing, etc. Moldsthus made are heated to predesigned elevated temperatures and become hotmolds. Cavity 10 in the molds 12 and 16 is used to make a casting.Cavity 14 in the mold 12 is used as a feeder or a downsprue where amolten metal is introduced to form the casting. A coolant is providedthrough devices 18 and 20 and applied on the solidifying casting. Thecoolant may first be applied at the distal end of the casting throughdevice 18 which is fixed between mold 12 and mold 16. The coolantdelivered from device 18 to the casting promotes the formation of afreezing front near the distal end of the casting. As soon as thefreezing front is formed at the distal end of the casting, the coolantcan then be applied through device 18 which travels from the distal endof the casting towards the feeder in cavity 14 to completely solidifythe metal. In some cases, device 20 is not needed. Coolant can bedirectly applied through device 18 as it progressively travels from thedistal end of the mold 12 to the feeder of the casting in cavity 14. Thespeed of the device 18 is defined as a relative translational speedbetween the device 18 and the molds 12 and 16. Such a relative motioncan be caused either by moving the device 18 while the molds arestationary, by moving the molds 12 and 16 while the device 18 isstationary, or by moving both device 18 and molds towards each other.The speed of the relative motion can be either constant or timedependent for either removing porosity completely or for controllingporosity distribution in the solidified casting. The temperaturedistribution in molds 12 and 16 can also be controlled for controllingporosity distribution in the final solidified casting.

FIG. 2 depicts the operation of producing a large thin-walled sandcasting with high internal integrity using the present invention of HMPCtechnology. When coolant is applied through the hot molds 12 and 16 onthe solidifying casting 24 as described in the paragraph

, freezing fronts are formed and move towards the feeder in the casting24. Two important freezing fronts are illustrated in FIG. 2 . Thesolidus front 20 is closer to the coolant delivery device 18 and therigid dendrite front 22 is further away from the coolant deliver device18. A dendrite network is considered as rigid when the fraction solid isabout 0.25, which is also the dendrite coherency point. Therefore, therigid dendrite front is also termed as the front of the dendritecoherency point.

There are two features shown in FIG. 2 that are closely related toporosity formation. One is the angle between the normal direction of thefront to the central line 26 along the casting wall thickness. The otheris the distance between these two fronts, 20 and 22.

For each front, there is an average angle of the front to the centralline 26 along the casting thickness. The temperatures of the molds 12and 16 and the coolant conditions including the coolant amount and thespeed at which the coolant delivery device 18 travels should becontrolled such that the average angle of the front 20 has to be greaterthan a critical value. When the average angle is greater than thecritical value, solidification shrinkage of the front 20 can be fed bythe liquid from the feeder so that shrinkage porosity can be avoided ifthe distance between these two fronts is small. For a controlleddistribution of porosity in the casting, the mold temperatures and thecooling conditions have to be controlled such that the average angles inthe regions where shrinkage porosity has to be maintained small or thedistance between two fronts has to be large.

The distance between the fronts shown in FIG. 2 affects the ease ofliquid feeding to the solidification shrinkage at front 20. Dendritesexisting between these two fronts tend to restrict the liquid ahead offront 22 to flow towards front 20. The use of hot molds in this presentinvention is to reduce the distance between these two fronts so that theliquid ahead of front 22 has less difficulties in feeding thesolidification shrinkage at front 20.

FIG. 3 illustrates a plate-shaped casting, the mold assembly, and thelocations and orientation of the tensile samples taken from theplate-shaped casting for mechanical property measurement. The thickness,width, and the length of the casting were 13 mm, 70 mm, and 400 mm,respectively. The length to thickness ratio of the plate-shaped castingwas about 31, much greater than 4-10, indicating that shrinkage porosityshould form in the casting under conventional sand casting conditions.A356.2 aluminum-silicon hypoeutectic alloy was used to make theplate-shaped casting to demonstrate the benefits of the presentinvention of HMPC process over sand casting and ablation castingprocesses.

FIG. 4 shows the relationship between the fraction solid and temperaturefor A356.2 alloy. The primary dendrite phase, which is a fcc phase,forms at about 615° C. where the fraction solid is zero. The eutecticsilicon phase forms at the eutectic temperature, T_(EU), about 572° C.where the fraction solid is about 0.5. Below the eutectic temperature, anumber of intermetallic phases form. The solidus temperature of thealloy is about 550 to 560° C. where the fraction of solid is 1.0 [23].

A validated model [15, 22] was used to calculate the cooling curves ofthe plate-shaped casting under conventional sand casting conditions andHMPC conditions by applied ablation cooling at a constant translationalvelocity of 10 mm/s from the distal end of the casting to thegate/feeder.

FIG. 5A illustrates the cooling curves of a sand casting. The moltenalloy at 680° C. is poured into the mold cavity. After mold filling asshown in FIG. 5A, the local temperature at the distal end of the castingdrops to the liquidus temperature, T_(L), in about 18 s, to T_(EU) inabout 80 s, then to the solidus temperature, T_(S), in about 160 s aslocal solidification completes. The temperature at the gate/feeder dropsslower than that at the distal end of the casting. There is atemperature plateau at T_(EU) on both cooling curves. The evolution offraction solid in the sand casting during 55 to 80 s after mold fillingis shown in FIG. 5B. There are a number of fronts illustrated in FIG.5B. The solidus front is shown as the gray front where the fraction ofsolid is 1. The eutectic front is outlined by the boundary betweenyellow and orange where the fraction solid is 0.5 and the correspondingtemperature is T_(EU). The dendrite coherency point is outlined by theboundary between red and brown where the fraction solid is 0.25according to Chai et al. [24]. For this alloy casting, the eutecticfront almost overlaps with the solidus front. One can use either thesolidus front or the eutectic front to represent front 20 and the frontof dendrite coherency point to represent front 22 shown in FIG. 2 . Itcan be clearly seen that when the solidus front just reaches the distalend of the plate-shaped casting, the front of dendrite coherency pointhas already entered the feeder/downsprue of the casting. The distancebetween these two fronts is the entire length of the casting, and thefraction solid in the entire casting is greater than 0.25. It isextremely difficult for the liquid in the feeder to flow throughdendrites over such a long distance to feed the solidification shrinkageof the solidus front. As a result, shrinkage porosity occurs in thecasting. FIG. 5C is a scanning electron microscopy (SEM) image of thefracture surface of a tensile specimen taken from the center section ofthe casting as shown in FIG. 3 . The SEM image reveals a few largeshrinkage pores on the fracture surface. The fracture surface is widelyaccepted as an ideal surface to show larger pores that are moredetrimental to the mechanical properties, especially ductility, thansmaller pores in a casting [25-26].

FIG. 6A illustrates the cooling curves of a sand casting and a HMPCcasting when the mold temperature is held at 100° C. The molten alloy at680° C. is poured into the mold cavity. Ablation cooling traveling at 10mm/s is then applied from the distal end of the casting starting atabout 80 s after the mold cavity is totally filled. Such conditions aresimilar to ablation casting [10-11] where the mold temperatures are atroom temperatures, slightly lower than 100° C. The cooling curves of thesand casting are represented by the black or red dashed lines. Thedashed cooling curves are similar to that shown in FIG. 5A except thatthe solidification times, the times from the moment of pouring to themoments when the cooling curves reach the solidus temperature, arelonger because the mold temperatures are slightly higher than thoseshown in FIG. 5A. The application of a progressive ablation coolingreduces the solidification times significantly as shown in the solidcurves in FIG. 6A. The evolution of fraction solid in the HMPC castingduring 55 to 80 s after mold filling is shown in FIG. 6B. The solidusfront appears at the distal end of the casting at 55 s while the frontof dendrite coherency point has already reached the middle of thecasting. The distance between these two fronts is increased at 60 s andthen is decreased afterwards. It appears that the feeder/downsprue iscapable of feeding the solidification of the solidus front when thefront moves close to the feeder towards the end of the castingsolidification. However, the majority portion of the casting, especiallythe middle portion of the casting, cannot be sufficiently fed. Shrinkageporosity does exist in the tensile specimens as shown in FIG. 6C.

FIG. 7A illustrates the cooling curves of a sand casting and a HMPCcasting when the mold temperature is held at 200° C. The molten alloy at680° C. is poured into the mold cavity. Ablation cooling traveling at 10mm/s is then applied from the distal end of the casting starting atabout 80 s after the mold cavity is totally filled. The cooling curvesof the sand casting, represented by the black or red dashed lines, aresimilar to those shown in FIGS. 5A and 6A except that the solidificationtimes are longer because the mold temperatures are higher. Theapplication of a progressive ablation cooling reduces the solidificationtimes significantly as shown in the solid curves in FIG. 7A, which isvery similar to the curves associated with ablation cooling in FIG. 6A.The evolution of fraction solid in the HMPC casting during 55 to 80 safter mold filling is shown in FIG. 7B. The solidus front reaches thedistal end of the casting at 55 s while the front of dendrite coherencypoint is within 1-2 thickness distance away from the solidus front,indicating that the liquid ahead of the front of dendrite coherencypoint is capable of feeding the solidification shrinkage of the solidusfront. The distance between these two fronts is increased to more than 4times the wall thickness of the casting when the cooling time is about70 s, but the distance then is reduced afterwards. Feeding problemscould occur for steel casting when the distance between these two frontsare greater than 4 times, but this is not a major concern for aluminumcasting. The SEM image, FIG. 7C, of the fracture surface shows only twosmall pores, indicating the internal quality of the aluminum HMPCcasting is reasonably good.

FIG. 8A illustrates the cooling curves of a sand casting and a HMPCcasting when the mold temperature is held at 350° C. The molten alloy at680° C. is poured into the mold cavity. Ablation cooling traveling at 10mm/s is then applied from the distal end of the casting starting atabout 80 s after the mold cavity is totally filled. The cooling curvesof the sand casting indicate that the solidification times in the sandcasting in molds of higher temperatures are longer than those in moldswith lower temperatures. However, there is no significant difference insolidification times of the HMPC castings solidified in molds held atdifferent temperatures. The evolution of fraction solid in the HMPCcasting during 55 to 80 s after mold filling is shown in FIG. 8B. Thesolidus front reaches the distal end of the casting at 55 s while thefront of dendrite coherency point is within 1-2 thickness distance awayfrom the eutectic front. In fact, the distance between these two frontsis within 1-2 times the thickness of the wall throughout the entiresolidification process of the plate-shaped casting, indicating that theliquid ahead of the front of dendrite coherency point is capable offeeding the solidification shrinkage of the solidus front. Indeed, theSEM image shown in FIG. 8C depicts no shrinkage porosity on the tensilesample taken from the center portion of the casting, indicating that theinternal quality of the HMPC casting is excellent, similar to that offorgings.

Results shown in FIGS. 5-8 suggest that the present invention of HMPCtechnology is capable of producing thin-walled castings free fromshrinkage porosity if the mold temperature is sufficiently high. Theinvention can also be used for controlling porosity distribution in acasting by varying the local temperatures since pores form in regionswhere the mold temperatures are lower and are eliminated in regionswhere the mold temperatures are higher. Porosity distribution in acasting can also be controlled by fixing the mold temperature andvarying the speeds of progressive cooling. Pores should form when thespeed is too low or too high.

The key idea of this present invention of HMPC technology is to controlthe mold temperature and the delivery of a coolant to the solidifyingcasting in such a manner that the distance between importantsolidification fronts is within a certain limit to eliminate porosityformation and outside the limit for allowing pores to form in thecasting. This limit seems to be in the range of 4 to 10 times thewall-thickness of the thin-walled casting. The use of a hot mold alsoensures that the large thin-walled casting can be filled by a moltenmetal so that extremely large sized castings can be made.

The invention further provides examples of the present invention of HMPCtechnology. The examples provided below are merely meant to exemplifyseveral embodiments and should not be interpreted as limiting the scopeof the claims, which are delimited only by the specification.

EXAMPLE

FIG. 3 illustrates a plate-shaped casting, the mold assembly, and thelocations and orientation of the tensile samples taken from theplate-shaped casting. The thickness, width, and the length of thecasting were 13 mm, 70 mm, and 400 mm, respectively.

2.5 kg of A356.2 alloy was melted in a graphite crucible using electricresistance heating, heated to 720° C. in 20 min, modified with 0.05 wt.%Sr, fully degassed while the melt cooled down from 720° C. to 680° C.before poured into the cavity in steel metal molds for making permanentmold castings, sand molds with sodium silicate as binder for making sandcastings, or preheated sand molds at various temperatures (100, 200, or350° C.) for making HMPC castings using the HMCPC technology describedin one embodiment of this present invention. Silica sand withconventional sodium silicate binder was mixed in a sand mixer for makingsand molds.

For comparison, forgings of the same dimensions of the plate-shapedcasting were obtained. These forgings were plastically deformed, at highforging temperatures, by 70% along its wall thickness to close out anycavities that might exist and to breakup silicon particles into smallfragments.

Molds for the HMPC process were preheated in a muffle furnace to desiredtemperatures. The preheated molds were then filled with the A356.2 alloyand transferred to an ablation cooling setup shown in FIG. 9 for makingplate-shaped castings. The ablation cooling setup consisted of an arrayof water nozzles and a translation conveyer traveling at rate of 10 mm/sover the filled molds, ablating away the sand molds to cool thesolidifying casting. Castings made are shown in FIG. 10 . Ablationcooling technology [10-11] failed to ablate the sand molds held at roomtemperatures under controlled manner. As a result, no castings withsatisfactory surface quality were successfully made by ablation coolingwhen the molds containing silica sand with a conventional binder were atroom temperatures.

FIG. 11 shows the tensile strength of the forgings and castings madeusing various processes where TM is the mold temperature. Castings withsatisfactory surface quality were made when TM was 100° C. or higher.Generally, the tensile strength obtained on this alloy was lower thanthose reported in the literature partly because the mass of metal meltedwas only 2.5 kg in this example. It is very difficult to refine moltenaluminum of small quantity.

FIG. 12 illustrates the ductility of the forgings and castings madeusing various processes where TM is the mold temperature. Castings withsatisfactory surface quality were made when TM was 100° C. or higher.The elongation of the sand casting and metal mold casting were around 3%or less. The HMPC process with mold temperatures higher than 200° C. iscapable of increasing the elongation of the thin-walled plate-shapedcasting to 16-19%. Such an elongation level is very close to that of theforgings and is 8 times greater than that of the sand casting.

While the invention has been described in connection with specificembodiments thereof, it will be understood that the inventivemethodology is capable of further modifications. This patent applicationis intended to cover any variations, uses, or adaptations of theinvention following, in general, the principles of the invention andincluding such departures from the present disclosure as come withinknown or customary practice within the art to which the inventionpertains and as may be applied to the essential features herein beforeset forth and as follows in scope of the appended claims.

REFERENCES

1. Q. Han, Dendritic Features of the Solidification Structure in a LargeAA3004 Direct Chill (DC) Cast Ingot, Metallurgical and MaterialsTransactions B, 2022, 02423-7.

2. Q. Han, J. Zhang, Fluidity of Alloys Under HPDC Conditions: FlowChoking Mechanisms, Metallurgical and Materials Transaction B, 51 (2020)1795-1804.

3. D. Sui, and Q. Han, “Effects of Different Parameters on PorosityDefects between the Horizontal and Vertical Shot Sleeve Processes,”International Journal of Metalcasting, 13 (2), (2019) 417-425.

4. Q. Han, C. Vian, and J. Good, Application of Refractory Metals toFacilitate Hot Chamber Aluminum Die Casting, International Journal ofMetalcasting, 15 (2), (2021) 411-416.

5. Q. Han, Shrinkage Porosity and Gas Porosity, Vol. 15, Casting, ASMHandbook, (ASM International, Materials Parks, Ohio 2008), pp. 370-374.

6. Q. Han, A Model Correlating Fluidity to Alloy Variables inHypoeutectic Alloys, Acta Materialia, 2022, 117587.

7. Q. Han, and H. Xu, “Fluidity of Alloys under High Pressure DieCasting Conditions”, Scripta Materialia, 53 (1) (2005) 7-10.

8. D. Sui, Z. Cui, R. Wang, S. Hao, and Q. Han, “Effect of CoolingProcess on Porosity in the Aluminum Alloy Automotive Wheel duringLow-Pressure Die Casting,” International Journal of Metalcasting, 10(2016) 32-42.

9. J. Campbell, Castings. Butterworth-Heinemann, 1991, p.188.

10. J. Grassi, J. Campbell, M. Hartlieb, and J. Major, “AblationCasting”, in Aluminum Alloys: Fabrication, Characterization, &Applications, eds. W. Yin & S.K. Das, (TMS, The Minerals, Metals, andMaterials Society, 2008), pp. 73-77.

11. J. Grassi, J. Campbell, M. Hartlieb, and J. Major, “The AblationCasting Process”, Materials Science Forum, 681-619 (2009) 591-594.

12. D. Weiss, J. Grassi, B. Schultz, and P. Rohatgi, “DiscoveringAblation: An Emerging Technology Known as Ablation Can Achieve FineMicrostructure and Better Mechanical Properties in Casting Alloys”,Metal Casting Design & Purchasing, Jan/February 2012, pp. 36-39.

13. D. Weiss, J. Grassi, B. Schultz, and P. Rohatgi, “Ablation Castingof Hybrid Metal Matrix Composites”, AFS Transactions, 119 (2011) 35-41.

14. Q. Han, “Ablation Casting: Solidification Characteristics,Microstructure Formation, and Mechanical Properties”, InternationalJournal of Metalcasting, 15 (2021) 1213-1222.

15. D. Sui, Q. Han, “Modeling Ablation Casting”, International Journalof Metalcasting, 16(1) (2022) 132-142.

16. V. Bohlooli, M. Shabani, and S.M.A. Boutorabi, “Effect of AblationCasting on Microstructure and Casting Properties of A356 AluminumCasting Alloy”, Acta Metallurgica Sinica, 26 (2013) 85-91.

17. M. Tiryakioglu, P. Eason, J. Campbell, “Fatigue Life ofAblation-Cast 6061-T6 Components”, Materials Science & Engineering A,559 (2013) 447-452.

18. M. Taghipourian, M. Mohammadaliha, S. M. Boutorabi, and S. H.Mirdamadi, “The Effect of Waterjet Beginning Time on the Microstructureand Mechanical Properties of A356 Aluminum Alloy during the AblationCasting Process”, Journal of Materials Processing Technology, 238 (2016)89-95.

19. P. Dudek, A. Fajkiel, and T. Regula, “The Research on the AblationCasting Technology for Aluminum Alloys”, Solid State Phenomena, 223(2014) 70-77.

20. K. M. Gabrys, M. H. Kondracka, S. Puzio, J. Kaminska, and M.Angrecki, “The Influence of the Modified Ablation Casting on CastsProperties Produced in Microwave Hardened Moulds with Hydrated SodiumSilicate Binder”, Arch. Metall. Mater., 65 (2020) 497-502.

21. L. Wang, R. Lett, S. Felicelli, J. Berry, J. Jordon, and D. Penrod,“Microstructure and Performance of Four Casting Processes for MagnesiumAlloy AZ91”, International Journal of Metalcasting, 5 (2011) 37-46.

22. J. Wu, D. Sui, and Q. Han, “High Quality Plate-Shaped A356 AlloyCasting by a Combined Ablation Cooling and Mold Heating Method”, Journalof Materials Processing Tech., 303 (2022) 117536.

23. Q. Han, and S. Viswanathan, “The Use of Thermodynamic Simulation forthe Selection of Hypoeutectic Aluminum-Silicon Alloys for Semi-SolidMetal Processing,” Materials Science and Engineering A, 364 (1-2), 2004,pp. 48-54.

24. G. Chai, L. Bäckerud, and L. Arnberg, “Relationship between GrainSize and Coherency Parameters in Aluminum Alloys, Materials Science andTechnology, 11 (1995) 1099-1103.

25. A.M. Gokhale, and G.R. Patel, “Origins of Variability in theFracture-Related Mechanical Properties of a Tilt-Pour-Permanent-MoldCast Alloy”, Scripta Materilia, 52 (2005) 237-241.

26. C.D. Lee, “Effects of Microporosity on Tensile Properties of A356Aluminum Alloy”, Materials Science and Engineering A, 464 (2007)249-254.

What is claimed is:
 1. A process for the casting of metals and theiralloys, comprising of the steps of: preparing sand molds containing atleast an aggregate and a binder to form a cavity to make castings;bringing at least one mold to predetermined elevated temperatures with acertain temperature distribution; introducing a molten material into themold cavity to form castings; delivering a predetermined amount of aselected coolant at predetermined rates, times, and durations to contactthe surfaces of the solidifying casting and to maintain an acceptablelevel of progressive solidification from the distal end of a casting tothe riser or downsprue; and controlling the cooling of the casting tomaintain the distance between the dendrite front and the solidus frontwithin a predetermined range during the solidification of the casting bycontrolling the mold temperatures and the coolant cooling until themetal is totally solidified.
 2. The process of claim 1, where theheating of the mold is achieved by any method that is conventionallyused in the casting industry, including, but not limited to, torchheating, oven heating, and infrared heating.
 3. The process of claim 1,where the local temperatures of the mold can be managed by usinginsulation materials, exothermic materials, and embedded heating devicesin the mold, or by other means that are conventionally used in the metalcasting industry.
 4. The process of claim 1, where the mold temperatureis heated to in a range between 100° C. to the solidus temperature ofthe molten material.
 5. The process of claim 1 wherein the moldtemperature is heated to in a range between 200° C. to the solidustemperature of the molten material.
 6. The process of claim 1 whereinthe mold temperature is heated to in a range between 300° C. to thesolidus temperature of the molten material.
 7. The process of claim 1,where the molten material is introduced into the mold cavity by gravityor by pressure.
 8. The process of claim 1 wherein the coolant is aliquid, a gas, a mixture of gases, or a mixture of liquids and gasesthat contact the surface of the introduced metal to achieve high coolingrates at the region of contact until the metal is cooled topredetermined temperatures.
 9. The process of claim 1, where the contactregion of the coolant to the casting moves from the distal end to thefeeder of the casting at controllable speeds.
 10. The process of claim 9wherein the controllable speed is variable and is between a range of 0mm/s to 100 mm/s.
 11. The process of claim 9 wherein the controlledspeed is variable and is between a range of 2-40 mm/s.
 12. The processof claim 1, where the molten material is a molten aluminum alloy. 13.The process of claim 1, where the molten material is a molten magnesiumalloy.
 14. The process of claim 1, where the distance between thedendrite front and the solidus front along the centerline of the wall ofa solidifying casting is between a range of 1 to 10 times thewall-thickness of the casting.
 15. The process of claim 1, where thedistance between the dendrite front and the solidus front along thecenterline of the wall of a solidifying casting is between a range of 4to 10 times the wall-thickness of the casting.
 16. A process for thecasting of metals and their alloys, comprising of the steps of:preparing sand molds containing at least an aggregate and a binder toform a cavity to make castings; bringing at least one mold topredetermined elevated temperatures with a certain temperaturedistribution; introducing a molten material into the mold cavity to formcastings; delivering a predetermined amount of a selected coolant atpredetermined rates, times, and durations to contact the surfaces of thesolidifying casting progressively from the distal end of a casting tothe riser or downsprue; and controlling the cooling of the casting tomaintain the openness of the feeding channel for the liquid from thefeeder to feed the solidification shrinkage of the casting bycontrolling the mold temperatures and the coolant cooling until themetal is completely solidified.
 17. The process of claim 16 wherein thecoolant is a liquid, a gas, a mixture of gases, or a mixture of liquidsand gases that contact the surface of the introduced metal to achievehigh cooling rates at the region of contact until the metal is cooled topredetermined temperatures.
 18. The process of claim 16, where the moldtemperature is heated to in a range between 100° C. to the solidustemperature of the molten material.
 19. The process of claim 16 whereinthe coolant is delivered to the surfaces of the casting progressivelytowards the feeder with speeds, constant or variable, between the rangeof 0 mm/s to 100 mm/s.
 20. The process of claim 16 wherein the coolantis delivered to the surfaces of the casting progressively towards thefeeder with speeds, constant or variable, between the range of 2 mm/s to40 mm/s.